Sine generation with variable frequency and amplitude

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Ozgur
Ozgur 2011-7-8
评论： Chaithra Kc 2020-1-23
Hi everyone,
I have been trying to write a code that generates series of sine wave with changing frequency and amplitude; for example a 20 Hz sine wave for 20 seconds, after it reaches to 30 Hz for 10 seconds and so on.
When with constant ouput values, there is no problem. The code I wrote for it is below
k=zeros(1,100);
t=zeros(1,100);
t=0:99;
for i=1:100;
if i<=30;
k(i)=1;
else if i<=60;
k(i)=3;
else i<=100;
k(i)=2;
end
end
end
plot(t,k)
It gives correct results. Try this one and imagine I want to change these constant values with sine waves.
When I changed k(i) values with sine, like below;
k=zeros(1,100);
t=zeros(1,100);
t=0:99;
a=linspace(0,2*pi,30);
for i=1:90;
if i<=30;
k(i)=2*sin(a);
else if i<=60;
k(i)=sin(a);
else i<=90;
k(i)=3*sin(a);
end
end
end
plot(t,k)
It gives that error;
??? In an assignment A(I) = B, the number of elements in B and I must be the same.
Error in ==> Untitled3 at 9 k(i)=2*sin(a);
The dimensions match, Can anyone give me a hand about the code above or show any other way?
Thanks,
Ozgur Palaz

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采纳的回答

Ozgur
Ozgur 2011-7-8
I think i solve the problem. Here is the code if you are interested;
num=length(t);
k=zeros(1,num);
f1=0.8;
f2=1;
f3=0.5;
fs=100;
T=1/fs;
for i=1:num;
if i<=num/5;
k(i)=2*sin(2*pi*f1*t(i));
else if i<=2*num/5;
k(i)=0;
else if i<=3*num/5;
k(i)=sin(2*pi*f2*t(i));
else if i<=4*num/5;
k(i)=0;
else i<=num;
k(i)=3*sin(2*pi*f3*t(i));
end
end
end
end
end
plot(t,k)
  1 个评论
Chaithra Kc
Chaithra Kc 2020-1-23
I have tried this the code is working but, I'm not able to generate it in the scope. The waveform is as shown in the picture...please help

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更多回答（3 个）

Friedrich
Friedrich 2011-7-8
Hi,
You get this error because sin(a) is a vector of size 1x30 and you want assign this to a single field k(i). Maybe give k an other size
k=zeros(100,30)
and than do
k(i,:)=2*sin(a)
  3 个评论
显示 1更早的评论
Friedrich
Friedrich 2011-7-8
Sorry my fault this would be correct:
k=zeros(1,100);
t=zeros(1,100);
t=0:99;
a=linspace(0,2*pi,30);
for i=1:90;
if i<=30;
k(i)=2*sin(a(i));
else if i<=60;
k(i)=sin(a(i-30));
else i<=90;
k(i)=3*sin(a(i-60));
end
end
end
but the code from andrei is much better.
Ozgur
Ozgur 2011-7-8
hanks, it results like Andrei suggested. Now I'm tryin on setting the sine frequency in the form of Sin(2*pi*f*t)
Time vector t should have been put into the for loop for this I guess.
Do you have any suggestion about that? Check this link to get what i am trying to manage.
<http://imageshack.us/photo/my-images/20/signalq.jpg/>
Thanks again.
Ozgur

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Andrei Bobrov
Andrei Bobrov 2011-7-8
k= zeros(1,100);
k(1:90) = sin(linspace(0,2*pi,30))'*[2 1 3];
EDIT
k= zeros(30,100);
k(:,1:90) = reshape(permute(repmat(sin(linspace(0,2*pi,30))'*[2 1 3],[1,1,30]),[1 3 2]),30,[]);
answer on comment
1. '*[2 1 3]
eg.:
>> a = (1:3)'
a =
1
2
3
>> b = [2 1 3]
b =
2 1 3
>> a*b
ans =
2 1 3
4 2 6
6 3 9
or
>> bsxfun(@times,a,b)
ans =
2 1 3
4 2 6
6 3 9
2. Please specify question
  2 个评论
Ozgur
Ozgur 2011-7-8
Thank you for your reply, this creates a sine wave and the error is gone, can you explain more detailed about this '*[2 1 3] expression?
Do you have any idea about how can I set the frequencies of the sine waves, can i do it with "t" and a "f" variable that are put into the format of sine SIN(wt)?
Thanks for your help...
Ozgur
Ozgur 2011-7-8
.
.
.
.
.
Your edit resulted different as Friedrich did before; like below;
http://imageshack.us/photo/my-images/20/signalq.jpg/
The signal i want to get is alike below figure please check it.
http://imageshack.us/photo/my-images/20/signalq.jpg/
Now, the question is about the frequencies. Let me say the first freq of the sine is 10 hz, second and the third is 50 and 20 Hz respectively.
how can i get the values into the code?
As you know, sinus is in the format of SIN(2*pi*f*t) where f is freq in Hz and t is time in sec. Should be there a sampling freq? I'm trying hard on this and i couldn't manage.
Ozgur

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Ozgur
Ozgur 2011-7-8
The sine waves i want to realize is alike below figure, I made it on Microsoft paint, so it is a little rough..
http://imageshack.us/photo/my-images/20/signalq.jpg/
Ozgur

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